1. Field of the Invention
The present invention relates to a magnetic head used to make the recording, reproducing and erasing of information in a magnetically recording system such as floppy disc drive, hard disc drive or the like.
2. Description of the Related Art
FIG. 7 is an perspective exploded view of the primary parts of a conventional magnetic head. The magnetic head shown herein comprises, as its primary components, a core chip 10, a slider piece (small) 12 and a slider piece (large) 4, the core chip being sandwiched between these slider pieces 12 and 14.
The core chip 10 is made of ferrite and includes a recording and reproducing gap 16 and an erasing gap 18 all of which are formed on the core chip 10 at the top thereof.
On the other hand, the slider pieces 12 and 14 are formed of calcium titanate ceramics and form a slider 20.
The slider pieces 12 and 14 are adhered to the core chip 10 respectively at its opposite sides by any suitable adhesive means such as organic adhesive or inorganic glass to form a magnetic head.
FIG. 8 is a perspective view of the magnetic head thus formed.
Since the slider 20 is defined by two parts, that is, the slider piece 12 and the slider piece 14, such a conventional magnetic head requires that the respective parts are machined separately. On manufacture, there are required a series of operations such as installation of the core chip 10 between the slider pieces 12 and 14, polishing of the mating surfaces of the core chip 10 and slider pieces 12, 14 and others. This contributes to increase of manufacturing cost in the entire system.
In order to overcome such a disadvantage, a magnetic head including a slider integrally moulded thereinto as shown in FIGS. 9A to 9C has been developed (see Japanese Patent Laid-Open No. 62-217413, for example).
FIG. 9A shows an integrally moulded slider 120 having a top face 120a in which a core chip holding aperture 122 is opened. The core chip holding aperture 122 is of a rectangular cross section corresponding to the configuration of the core chip 110. The core chip holding aperture 122 extends downwardly from the top face 120a of the slider 120 therethrough.
The core chip holding aperture 122 receives the core chip 110 shown in FIG. 9B initially from the side of legs 111 thereof. The core chip 110 is fixed to the slider 120 by the use of a rod of inorganic glass 124 .shown in FIG. 9C. More particularly, the inorganic glass rod 124 is fused after it has been located between the outer wall of the core chip 110 and the inner wall of the core chip retaining aperture 122. As a result, the core chip 110 will be firmly adhered to the inner wall of the core chip holding aperture 122.
When the core chip 110 is mounted in and adhered to the slider 120 as described above, the core chip 110 may take its various different positions relative to the core chip holding aperture 122, as shown in FIGS. 10A, 10B and 10C. As seen from FIG. 10A, for example, the core chip 110 may be located closer to one of the shorter sides of the aperture 122. The core chip 110 may be differently positioned closer to one of the longer sides of the aperture 122, as seen from FIG. 10B. Furthermore, the core chip 110 may be disposed skewedly within the core chip holding aperture 122, as shown in FIG. 10C.
If the core chip is simply inserted into the core chip holding aperture 122 as described above, it is difficult to maintain a clearance between the core chip 110 and the aperture 122 equally from one slider to another slider. If a core chip 110 is skewedly located within the core chip holding aperture 122, more concretely, the minimum clearance becomes about one microns while the maximum clearance is ranged between about 20 microns and about 30 microns. In such a situation, if the core chip 110 is adhered to the core chip holding aperture 122, it is required at the minimum clearance that an inorganic glass rod 124 is fused at a higher temperature and for a longer time period than those required in an inorganic glass rod at the maximum clearance so that the molten glass rod can enter the minimum clearance very well.
FIG. 11 shows a graph representing the relationship between the magnitude of clearance and the velocity of entrance of glass into the clearance. In this graph, the vertical axis represents the velocity of entrance v and the horizontal axis represents the magnitude of clearance d where the temperature of fusion and the material of glass are invariable. As will be apparent from this graph, the smaller the magnitude of clearance, the lower the velocity of entrance of glass.
If the factors relating to temperature and time are set relative to smaller magnitudes of clearance, thus, the molten amount of inorganic glass rod 124 will unnecessarily overflow out of the maximum clearance. On the other hand, if these factors are set to larger magnitudes of clearance, the molten inorganic glass rod 124 will not sufficient enter the minimum clearance, resulting in imperfect adhesion.
Even if the slider is formed into one piece, any adjustment of clearance is required. However, even such an adjustment of clearance cannot easily aid to mount the core chip in the core chip retaining aperture precisely.
There is also known a magnetic head which comprises a slider and a shield ring disposed to surround the outer periphery of the slider. The slider is made of calcium titanate ceramics or barium titanate ceramics while the shield ring is made of permalloy or the like.
For example, a floppy disc drive generates electromagnetic noises from a spindle motor used as a drive source for rotating the floppy disc, a pulse motor used as a drive source for moving a magnetic composite head to a desired track across the rotating floppy disc and their drive circuits.
Further, word processors and personal computers which are provided with floppy disc drives generally include a CRT display which generates strong electromagnetic noises.
If the electromagnetic noises enter the core, its S/N ratio (ratio of signal to noise level) may be degraded and the symmetry in write waveform may be disturbed. These phenomena can create errors on reading.
The shield ring is for preventing the electromagnetic noises from reaching the composite magnetic core. For limitation in respect to available space, the thickness of the shield ring cannot be increased indefinitely. It is thus customary to make the shield ring from a sheet material having a thickness of about 0.2 mm.
In view of easy workability, the shield ring is frequently manufactured by means of bending or deep drawing. This is a reason why the material of the shield ring is generally permalloy.
Although the permalloy has a large magnetic permeability over a wide range from direct current to low frequency region, however, its magnetic permeability is decreased in high frequency region from several tens to several hundreds kHz which is utilized on writing and reading in the conventional floppy disc drive. It is thus impractical to use the magnetic shield ring formed of permalloy in shielding any electromagnetic noise mentioned above.